D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere

D21C9/001—Modification of pulp properties

D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives

D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere

D21C9/10—Bleaching ; Apparatus therefor

Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

Abstract

The present invention relates to lyocell fibers having varying cross sections and diameters along and between rough surfaces and fibers seen at high magnification. This fiber is produced by centrifugal spinning, meltblowing or spunbonding. Fibers are produced in the microdenier range with an average weight of 1 denier or less. This fiber can be formed from yarns that form a low gloss and very soft hand fabric. Alternatively, the fibers may be formed of a self-woven nonwoven fabric.

Description

Lyocell Fiber {LYOCELL FIBERS}

The present invention relates to a lyocell fiber having novel properties and a method of manufacturing the same. New properties include surface shapes such as variable diameters along fiber length. The present invention relates to yarns made from such fibers, to wovens and nonwovens comprising such fibers. In particular, the method includes the step of dissolving cellulose in amine oxide to form a dope. The latent fibers are made by extruding the dope into the air stream through the small holes or centrifugally releasing the dope through the small holes. The latent fibers are regenerated in liquid non-solvent to form fibers. Any process can be used to make self-bonded nonwovens. The method of the present invention imparts unique surface properties to lyocell fibers that are distinguished from traditional continuous drawn fibers.

Strong regenerated cellulose fibers have been produced by viscose and copper ammonium processes during the first century. The cupra process was patented in 1890 and the viscose process was patented two years later. In the viscose process, cellulose is soaked in mercury caustic soda solution to form alkaline cellulose. It reacts with carbon disulfide to form cellulose xanthate, which is dissolved in dilute caustic soda solution. After filtration and degassing, the xanthate solution is extruded from the submerged spinneret into a regeneration bath consisting of sulfuric acid, sodium sulfate, zinc sulfate and glucose to form a continuous filament. The resulting viscose rayon is currently used in fabrics and widely used as reinforcement in rubber products such as tires and drive belts.

Cellulose is soluble in ammonia-containing copper oxide solutions. This property forms the basis of copper ammonium rayon production. The cellulose solution is introduced into a 5% caustic soda or dilute sulfuric acid solution through submerged spinnerets to form fibers. After copper removal and cleaning, the resulting fiber has a large wet strength. Copper ammonium rayon is available for very thin denier fibers and is used almost exclusively in textiles.

Recently other cellulose solvents have been developed. One such solvent is based on a nitrogen tetraoxide solution in dimethylformamide. Although much research has been conducted, the process of forming regenerated cellulose fibers using such solvents has not been commercialized.

The usefulness of tertiary amine N-oxides as cellulose solvents has been known for some time. US Patent 2179181 (Graenacher) discloses amine oxide materials suitable as solvents. However, this patent can only form low concentration cellulose solutions and raises the issue of solvent recovery. US Patent 3447939 (Johnson) discloses the use of anhydrous N-methylmorpholine-N-oxide (NMMO) and other amine N-oxides as solvents for cellulose and many other natural and synthetic polymers. This solution has a relatively low solids content. US Patent 3508941 (Johnson) discloses a method of mixing various natural and synthetic polymers in solution to form an intimate blend with cellulose. Non-solvents for celluloses such as dimethylsulfoxide are added to reduce the dope viscosity. The polymer solution is spun directly in cold methanol, but the resulting filaments are of fairly low strength.

In early 1979, however, a patent was issued to produce regenerated cellulose fibers using various amine oxides as solvents. In particular N-methylmorpholine-N-oxide in which about 12% water is present has proved to be a useful solvent. Under conditions of heating to 90-130 ° C., cellulose is dissolved in a solvent and extruded from multiple fine-pore spinnerets or disks into non-precipitating fluids such as air or nitrogen. Cellulose-doped filaments are drawn continuously according to a rotation-elongation ratio of 3-10 to cause molecular orientation. They are then introduced into a non-solvent fluid, usually water, to regenerate cellulose. Other regeneration solvents, such as lower aliphatic alcohols, have also been proposed. The process is described in U.S. Patent 4142913; 4144080; 4211574; 4246221; 4416698 (McCorsley). U.S. Pat.Nos. 5252284 (Jurkovic) and 5417909 (Michels) deal with the shape of extrusion nozzles for spinning cellulose dissolved in NNMO. US Patent 4426228 (Brandner) discloses the use of various compounds that act as stabilizers to prevent cellulose or solvent degradation in heated NNMO solutions. U.S. Patents 4145532 and 4196282 (Franks) address the difficulty of dissolving cellulose in amine oxides to achieve high concentrations of cellulose solutions.

The cellulose fabric yarn spun from NMMO solution is called lyocell fiber. Lyocells are a general term for fibers composed of cellulose precipitated from organic solutions without the substitution of hydroxyl groups and no chemical intermediates formed. Lyocell products manufactured by Courtaulds, Ltd. are available from Tencel Fiber. This fiber is available from 0.9-2.7 denier. Denier is the weight (g) of 9000 meters of fiber. Due to its fineness, the yarn produced produces a pleasantly textured fabric.

One limitation of currently produced lyocell fibers is their shape. They are continuously mechanically drawn and have a generally uniform, round or oval cross section and lack crimp and have a relatively smooth and shiny surface when spun. It is difficult to achieve uniform separation in carding processes and is less ideal as staple fibers as it can lead to heterogeneous mixing and yarns. To solve the straight fiber problem, the artificial staple fibers are crimped in a sub-process prior to chopping. An example of crimping is in US Pat. No. 5591388 or 5601765 (Sellars) where the fiber tow is compressed in a stuffer box and heated with dry steam. Fibers with continuous uniform cross sections and shiny surfaces also produce yarns of plastic appearance. Yarns made of thermoplastic polymers frequently require the addition of a gloss remover such as titanium dioxide prior to spinning. U. S. Patent 5417909 (Michels) discloses the use of spinnerets to produce lyocell fibers with non-circular cross sections, but this method has not been commercialized.

Two widely recognized problems in forming lyocell fibers result from fibrillation of the fibers under wet wear conditions that may occur during washing. Fibrillation causes pilling, ie entanglement into fibrillated, small, relatively dense balls. Fibrillation also produces a whitened appearance in dyed fabrics. Fibrillation is caused by high orientation and poor side cohesion in the fiber. This problem is described in morttimer, S.A. & A.A. Peguy, Journal of Applied Polymer Science, 60: 305-316 (1996) and Nicholai M., A. Nechwatal & K. P. Mieck, Textile Research journal, 66 (9): 575-580 (1996). The first was to solve the problem by varying the residence time in the air gap zone between temperature, relative humidity, gap length, and extrusion and decomposition. Nicholai et al suggest fiber crosslinking, but "... technical implementation is unlikely to be possible." Related U.S. Patents are: 5403530, 5520869, 5580354, 5580356 (Taylor); 5562739 (Urben); 5618483 (Weigel). These patents treat fibers with reactive materials to induce surface modification or crosslinking. Enzymatic treatment of yarns or fabrics is currently the preferred method of reducing the problems caused by fibrillation. However, all the treatments mentioned above have disadvantages and add cost. Fibers resistant to fibrillation would be a significant advantage.

Low denier fibers were made from synthetic polymers by various extrusion processes. Three of these relate to the present invention. One is melt blowing. The molten polymer is extruded through a series of small pores into a stream of air flowing parallel to the extruded fibers. This stretches the fiber when it is cooled. Kidneys have two functions. Elongation gives longitudinal molecular orientation and reduces the final fiber diameter. A similar process is spunbonding of fibers extruded into tubes and elongated by air flow through the tubes caused by vacuum at the far end. Generally, spunbonded fibers are longer than shorter length discrete melt blown fibers. Another process called centrifugal spinning differs in that the molten polymer is released from a hole in the side wall of a rapidly rotating drum. As the drum rotates, the fibers stretch slightly due to air resistance. But there is no strong airflow present in meltblowing. All three processes are used to make nonwovens and do not use a method of mechanically drawing fibers continuously. There have been numerous patents since commercially important over the years. US Patent 3959421 (Weber) and 5075068 (Milligan). The Weber patent sprays water on a gas stream to quench the fibers. A related patent is WO91 / 18682 which discloses a method of coating paper by modified meltblowing. The coating materials shown are starch, carboxy-methylcellulose, polyvinyl alcohol, aqueous solutions of latex, bacterial cellulose suspensions, aqueous materials, solutions or emulsions. However, this process sprays the extruded material rather than forming it into latent fibers. U. S. Patents 5589125 and 5607639 (Zikeli) direct airflow across extruded lyocell dope strands when leaving the spinneret. The airflow only cools and does not stretch the filament.

Centrifugal spinning is exemplified in US Pat. No. 5,242,633, 5326241 (Rooks). In US Patent 4440700 Okada announces the centrifugal spinning process of thermoplastics. As the material is released, the fibers are trapped in an annular form, which is moved downwards by the cooling liquid curtain flowing around the spinning head. Suitable polymers for this process are polyvinyl alcohol and polyacrylonitrile. In the case of these two materials it is wet spun in solution and the coagulation bath replaces the cooling liquid curtain.

Since cellulose itself is insoluble in nature, except Kaneko, processes belonging to meltblowing, spunbonding and centrifugal spinning have not been used for cellulose materials.

Very fine fibers, called microdenier fibers, have deniers of 1.0 or less. Melt blown fibers made of various synthetic polymers such as polypropylene, nylon, or polyester are available in diameters as small as 0.4 μm (about 0.001 denier). However, the tenacity of these fibers is small and poor water absorption is a negative factor when they are used in cloth fabrics. Microdenier cellulose fibers as thin as 0.5 denier were produced only by the viscose process.

The process of the present invention provides new lyocell fibers that overcome the limitations of synthetic polymers, rayon and lyocell fibers currently available. This allows the formation of low denier fibers. At the same time, as can be seen at high magnification, the surface of each fiber is rough and the fibers have cross-sections of varying shapes and diameters along the length, have significant natural creases and resist fibrillation under wet wear conditions. All of these are absent in lyocell fibers produced by processes using continuous mechanical drawing means.

1 is a block diagram of steps used in practicing the present invention.

2 is a partial cutaway perspective view of a typical centrifugal spinning facility used in the present invention.

3 is a partially cutaway perspective view of a meltblowing facility used in the present invention.

4 is a cross-sectional view of the extrusion head used in the meltblowing apparatus.

5 and 6 are scanning electron micrographs 100 and 10000 times that of commercial lyocell fibers.

Figure 14 shows the production of self-bonded lyocell nonwovens using a centrifugal spinning process.

15 and 16 are 1000-time scanning electron micrographs of two commercial fibers showing fibrillation caused by the wet wear test.

Figures 17 and 18 are 1000-time scanning electron micrographs of two fibers made by the method of the present invention subjected to a wet wear test.

19, 20 and 21 are 100-, 1000-, and 10000-fold scanning electron micrographs of lyocell fibers prepared by the meltblowing process.

The present invention relates to fibers made of regenerated cellulose having a variable diameter along the fiber length. Cellulose and regenerated cellulose include blends of natural and synthetic polymers in which cellulose is a major component of weight and soluble in cellulose and spinning solvents. In particular the invention relates to low denier fibers made from cellulose solutions in amine N-oxides by meltblowing or centrifugal spinning processes. Meltblowing, spunbonding and centrifugal spinning are processes similar to those used for the production of thermoplastic fibers even if cellulose is present in solution and the spinning temperature is elevated. Continuous drawing and continuous mechanical drawing refer to a lyocell fiber manufacturing process in which the fibers are first drawn mechanically through the air gap to elongate and then molecularly oriented through the regenerator.

The process of the present invention begins by dissolving the cellulosic stock in an amine oside, especially N-methylmorpholine-N-oxide (NMMO), in which some water is present. Such dope or cellulose solutions in NMMO are prepared by known techniques (by McCorsley or Franks). In the present invention, the dope is fed to the spinning device or the extruder at 90-130 ° C. by a pump at a somewhat elevated temperature. Finally, the dope is guided into the air through a number of small holes. In the case of meltblowing, the extruded yarn of cellulose dope is trapped in a disturbing gas stream flowing in a direction parallel to the filament path. When the cellulose solution is released through the hole, the liquid strands or potential filaments are stretched (or the diameter is reduced and the length is increased) during the continuous movement after leaving the hole. Disturbance leads to changes in natural folds and final fiber diameter along the length of each fiber. Variability along the fiber length can be quantified by microscopic examination of each fiber. This variability is measured by variability coefficient or CV. CV is calculated by obtaining the average diameter size. CV is the mean diameter standard deviation divided by the mean diameter. The resulting value is converted to a percentage by multiplying by 100%. The filaments made in accordance with the present invention exhibit CV values greater than the CV of the continuously drawn fibers. For example, the filaments of the present invention exhibit CV values of at least 6.5%, in particular at least 7%, even more than 10%. Continuously drawn fibers having a uniform diameter and without wrinkles and introduced in the post-spinning process show no high variability in fiber diameter as measured along the fiber length as compared to the fibers of the present invention. The fibers of the present invention have irregular wrinkles and have a peak-to-peak amplitude greater than one fiber diameter and a period greater than five fiber diameters.

Spunbonding is a type of meltblowing in that the fibers are stretched in the air stream without being trapped and mechanically pulled. In the present invention, belt blowing and spunbonding are considered equivalent.

When fibers are produced by centrifugal spinning, dope strands are released in the air through small holes and drawn by inertia imparted by the spinning head. The filament is then guided to the regeneration solution or the regeneration solution is sprayed onto the filament. The regeneration solution is a non-solvent such as water, lower aliphatic alcohols or mixtures thereof. NMMO used as a solvent can be recovered in the regeneration tank for reuse.

The disturbances and vibrations of air around potential fiber strands contribute to inherent geometry when produced by meltblowing or centrifugal spinning processes.

Filaments having an average size of 0.1 denier or less can be easily formed. Denier can be adjusted by several factors including hole diameter, gas flow rate, spinning head speed, and dope viscosity. The dope viscosity is cellulose D.P. And concentration factor. Fiber length can be controlled by the speed and design of the air flow surrounding the extrusion hole. Depending on the spinning conditions, continuous fibers or short staple fibers are produced. The facility can be easily modified to form individual fibers or to make them into cellulose nonwovens. In the latter case, mats are formed and self-bond before fiber regeneration. The fibers are recovered from the regeneration media and can be washed, bleached, dried and handled.

The gloss of the fibers formed according to the invention is much less than the continuous drawn lyocell fibers lacking the deglossing agent and thus do not have a plastic appearance. This is due to the inherent corrugated surface of the fiber which is evident in high magnification microscopy.

By appropriately adjusting the spinning conditions, the fibers produced according to the invention have a narrow fiber diameter distribution and variable cross-sectional shape. Changes in diameter and cross-sectional configuration occur along the length of each fiber, giving a greater CV than commercial lyocell fibers produced in a continuous drawing process. The fibers of the invention have high diameter variability along the fiber length in the case of regenerated cellulose fibers. The fibers of the present invention have a shape similar to natural fibers.

The fibers produced by meltblowing or centrifugal spinning according to the invention have different natural pleats than that imparted by the stuffer box. The pleats imparted by the stuffer box are very regular and have short peak to peak periods corresponding to amplitudes less than one fiber diameter and up to two or three fiber diameters. Fibers made in accordance with the present invention have an irregular amplitude greater than one fiber diameter and irregular periods and waveform appearances greater than five fiber diameters.

Surprisingly, the fibers of the present invention are highly resistant to fibrillation under wet wear conditions. This is advantageous in that post-spinning treatment such as crosslinking or enzyme treatment is unnecessary.

The properties of the fibers of the present invention are suitable for carding and spinning in traditional fabric manufacturing processes. Fibers with the properties of natural fibers can be produced with microdenier diameters that are not naturally obtainable. Fiber diameters as thin as 0.1 denier are possible in the present invention. It is also possible to directly prepare a self-bonded web or a tightly wound multi-yarn from the fibers of the present invention.

An advantage of the present invention is the ability to be considered non-compatible polymers and the ability to form blends of cellulose. Amine oxide is a powerful solvent that can dissolve not only cellulose but also other polymers. Thus, cellulose may be lignin, nylon, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylpyrrolidone, polyacrylic acid, starch, polyvinyl alcohol, polyester, polyketone, casein, cellulose acetate, amylose, amylopectin, cation Blend with starch. The homogeneous blend of cellulose allows these materials to produce fibers with new and unique properties.

It is an object of the present invention to provide a method for forming low denier regenerated cellulose fibers or cellulose blend fibers from solution in an amine oxide-water medium by meltblowing, spunbonding or centrifugal spinning rather than a continuous drawing process.

It is also an object of the present invention to provide low denier cellulose fibers with advantageous geometries and surface properties for forming yarns. This fiber shows a higher CV compared to lyocell fibers produced by a continuous drawing process.

It is also an object of the present invention to provide fibers with less natural wrinkles and gloss.

It is also an object of the present invention to provide lyocell fibers that are resistant to fibrillation under wet wear conditions.

It is another object of the present invention to provide regenerated cellulose fibers having properties beyond those of natural fibers. It is also an object of the present invention to provide a method for forming the above fibers by a process in which all preparation reagents can be easily recovered and reused.

The type of cellulose raw material used in the present invention is not critical. Bleached or unbleached wood pulp that can be produced by kraft, prehydrolyzed kraft, sulfurous acid processes is possible. Cellulose raw materials, such as purified cotton down, are also suitable. Prior to dissolution in the amine oxide solvent, the cellulose sheet is cut into fine fluff to promote dissolution.

The cellulose solution can be prepared in the manner of US Pat. No. 4246221 (McCorsley). For example, cellulose will be moistened in a non-solvent mixture consisting of 40% NMMO and 60% water. The weight ratio of cellulose to NMMO is 1: 5.1. The mixture is mixed in a double arm sigma blade mixer under vacuum for 1 hour at 120 ° C. until sufficient water is distilled off leaving 12-14% to NMMO to form a cellulose solution. The resulting dope contains about 30% cellulose. Or NMMO with an appropriate water content is initially used to eliminate the need for vacuum distillation. This is a convenient way to make spinning dope in the laboratory, and commercial NMMO at concentrations of 40-60% is mixed with laboratory reagent NMMO containing only 3% water to produce a cellulose solvent having a 7-15% water content. The moisture present in the cellulose should be taken into account when controlling the water present in the solvent. Methods for preparing cellulose dope in NMMO-water solvents are described by Chanzy, H. & A. Peguy, Journal of Polymer Science, Polymer Physics Ed., 18: 1137-1144 (1980) and Navard, P. & J.M. Published in the Haudin British Polymer Journal, p174, Dec. 1980.

1 shows the process steps of the present invention. Cellulose dope preparation in aqueous NMMO is known. What is not noticed is the way these dope is deposited. In the process of the invention the cellulose solution enters the disturbing air stream from the extrusion hole rather than directly into the regeneration bath as in viscose or cupra rayon. The potential filament is then regenerated. However, the process of the present invention differs from the traditional lyocell fiber manufacturing process since the dope is continuously drawn downward as a continuous yarn through the air gap and does not enter the regeneration tank.

2 shows a centrifugal spinning process. The heated cellulose dope 1 is guided to a heated hollow cylinder or drum 2 having a closed base and a plurality of holes 4 in the side walls 6. When the cylinder rotates, the dope exits horizontally through the hole as a thin thread (8). When the seals are subjected to the resistance of the surrounding air they are greatly drawn or stretched. The degree of elongation depends on easily controlled factors such as cylinder rotation speed, hole size, and dope viscosity. The dope strand is solidified into individual fibers oriented in the non-solvent 10 submerged in gravity or descended by gravity or downwardly by airflow. Alternatively, the dope strand 8 may be partially or completely regenerated by water spray from the spray nozzle 16 ring supplied by the regeneration solution source 18. They can also be formed into nonwovens before or during regeneration. Ethanol or water-ethanol mixtures are also useful but water is the preferred cohesive non-solvent. The fibers are collected, washed to remove residual NMMO, bleached and dried as necessary. Example 2 shows details of a yarn centrifugal spinning yarn manufacturing process.

3 and 4 show a typical meltblowing process. In FIG. 3 the dope source (not shown) is guided to the extruder 32 and the extruder directs the cellulose solution to the head 34 with a number of holes 36. Air or other gas is supplied through line 38 to enclose and transport the extruded solution strand 40. Tank 42 includes regeneration solution 44 where the strands are regenerated with cellulose fibers. Or the potential fiber is sprayed with water for regeneration. The degree of non-mechanical drawing or elongation depends on factors such as pore size, dope viscosity, cellulose concentration, air velocity, temperature and nozzle configuration.

4 shows a typical extrusion hole. Multiple holes 36 are drilled in the plate 20. It is secured to the body of the extrusion head 26 by a series of cap screws 18. The inner member 24 forms a cellulose solution extrusion port 26. An air passage 28 surrounding the extruded solution filament 40 draws the filament and transports it to the regeneration medium. Example 3 shows the details of the yarn meltblowing fiber manufacturing process.

The scanning electron micrographs of FIGS. 5-6 are for lyocell fibers prepared by a traditional continuous drawing process. Note the rounded configuration of the cross section along the fiber length for each fiber. Fibers with a uniform diameter along the fiber length have a low CV and the CV directly reflects the diameter variability. For some continuously drawn lyocell fibers (not shown) a value of 6.1% or less is observed. The 10000 times magnification surface of FIG. 6 is remarkably smooth.

7-10 show the fibers produced by the centrifugal spinning process of the present invention. The fibers of Figure 7 have a diameter range and are somewhat meandering to provide natural pleats. This natural wrinkle is different from the regular sinusoidal shape obtained in the stuffer box. The amplitude and period are irregular and are several times the fiber diameter in height and length. Most of the fibers are slightly flat and fairly twisted. The fiber diameter is 1.5-20 μm (<0.1-3.1 denier) and most of the fibers are clustered around the average diameter of 12 μm (1 denier). Other distinctive properties along with natural wrinkles are evident in the micrographs. For example, unlike the continuous drawn fibers of FIGS. 5 and 6, lyocell fibers produced by the centrifugal spinning process show more variability in cross section along the fiber length, resulting in high CV. This variability is more pronounced in centrifugal yarns than in other cases. Centrifugal spun yarns, however, exhibit higher diameter variability along the fibers as compared to continuous drawn fibers. In some centrifugal yarns (not shown) the CV is 10.9-25.4%.

However, lyocell fibers produced by the present invention can achieve variability of 6.5-25.4% and more. The following examples show the method used for this fiber decoction. By varying the process conditions, lyocell fibers have a coefficient of variability.

FIG. 8 shows the fiber of FIG. 7 at 10,000 times magnification. FIG. The surface is uniformly rough in appearance and differs from commercial fibers. This results in low gloss and improved spinning properties.

9-10 are scanning micrographs of fiber cross sections taken 5 mm away from a single centrifugal fiber. A change in cross section and diameter is shown along the fiber. This variability is a property of centrifugal spinning and meltblowing fibers.

11-12 are low and high magnification scanning micrographs of meltblowing fibers. The wrinkles of the sample compared to the centrifugal yarns are larger. The 10,000-fold photograph of Figure 12 shows a rough surface similar to centrifugal fibers. Like centrifugal spinning fibers, meltblowing fibers have higher diameter variability along the fiber length compared to fibers made in a continuous drawing process. In some meltblowing fibers (not shown) the CV is 12.6-14.8% or more.

The total results obtained from the experiments performed using various apparatus and conditions indicate that the fibers of the present invention can form fibers having a coefficient of variability of 6.5-24.5% and higher. These values are outside the ranges obtained for the continuous drawn fibers produced by TITK or for the fibers sold by Tencel.

Nevertheless, the overall shape of the fibers of the two processes has characteristics similar to those of natural fibers, which is very advantageous for forming fine and dense yarns. This is a unique aspect of the lyocell fibers of the present invention.

Figure 13 shows a method of making a self-bonding lyocell nonwoven using a modified meltblowing process. Cellulose dope 50 is fed to an extruder 52, followed by an extrusion head 52. When the dope strand 58 descends from the extrusion head, the air source 56 serves to draw the dope strand 58 at the extrusion hole. Process parameters are chosen such that the resulting fiber is a continuous fiber rather than a random short fiber. The fibers fall on the endless moving porous belt 60 which is supported and driven by the rollers 62, 64. An upper roller (not shown) is used to compress the fibers tightly and to bond at the intersections. The regeneration solution 68 is sprayed downward by the nebulizer 70 as the mat 66 proceeds along the path on the belt 60. At the end of the belt the regenerated product 72 is removed and subjected to further processing such as washing, bleaching and drying.

Figure 14 shows a process for forming self-bonded nonwovens using centrifugal spinning. The cellulose dope 80 is supplied to the rotating drum 82 which has many holes in the side wall. Potential fibers 86 are released through holes 84 and drawn or lengthened by inertia or air resistance imparted by the rotating drum. They impinge on the inner sidewalls of the receiver surface 88 located around the drum. The receiver may have a cone bottom 90. The regeneration solution 92 curtain flows downward from the ring 94 around the wall of the receiver 88 to partially agglomerate the cellulose mat impinged on the receiver side wall. The ring 94 is positioned as shown or moved downward if more time is needed for the potential fibers to self-bond into the nonwoven web. The partially agglomerated nonwoven web 96 is continuously mechanically drawn from the receiver bottom 90 into the agglomeration bath 98 of the vessel 100. As the web travels along the path it collapses into two flat ply nonwoven structures in a cylindrical shape. The web is held in the bath as it moves under the rollers 102, 104. The roller 106 removes the two ply webs 108 that are fully aggregated in the bath. The web 108 is then subjected to a washing or bleaching process continuously and dried for storage. It is divided into a single ply nonwoven or maintained as two ply materials.

Fibrillation is the division of a single fiber surface into microfibers or fibrils. Splitting occurs as a result of rubbing the fiber on a hard surface or as a result of wet wear of the fiber to the fiber. Depending on wear conditions, most of the fibrils remain attached to the parent fiber at one end. Fibrils are so fine that they are nearly transparent, giving the final fabric a white appearance. In the case of more extreme fibrillation, the microfibrils are entangled to provide an appearance.

There is no industry standard for measuring fibrillation resistance, but the following procedure is used. Weigh 0.003 g of individual fibers and place in a 25 mL test tube (13 x 110 mm) with a lid of 10 mL water. The sample is placed on a shaker operating at low amplitude at a frequency of 200 cycles per minute. The test period is 4-80 hours. The sample of Figures 15-18 is shaken for 4 hours.

Figures 15-16 show significant fibrillation caused in fibers made from commercial yarns obtained from two different sources. In comparison, Figures 17-18 show the case of the meltblowing fibers of the present invention.

19-21 show that fibrillation is very fine in meltblowing fibers. Although the reason is not fully understood, it is judged that the fiber of this invention has low crystallinity and orientation compared with the fiber by a well-known process. In addition to the reduced fibrillation tendency, the fibers of the present invention have more uniform dye solubility. There is no tendency to acquire a whitening appearance by fibrillation after use in the case of the present invention. Figure 19 shows the shape of the fiber of the present invention. In particular, diameter variability is apparent along the fiber length. Figure 21 shows the rough surface of the fiber of the present invention.

Example 1 Preparation of Cellulose Dope

The cellulose pulp used is standard bleached kraft southern softwood commercial pulp grade NB416 (Weyerhaeuser Company, New Bern, North Carolina). It has a 88-89% alpha cellulose content and a D.P. of 1200. Before use, the wood pulp sheet is passed through a fluff former and broken down into individual fibers and small fiber clumps. A 250 mL three neck glass flask was filled with 5.3 g fluff cellulose, 66.2 g 97% NMMO, 24.5 g 50% NMMO and 0.05 g propyl gallate. The flask is placed in an oil bath at 120 ° C. and stirring is continued for 0.5 hours. The resulting fluidity dope is used directly for spinning.

Example 2 Fabrication by Centrifugal Spinning

The spinning device used is a modified cotton candy type similar to U.S. Patent 5447423 (Fuisz). The rotor preheated to 120 ° C. is 89 mm in diameter and rotates at 2800 rpm. By blocking the holes, the number of holes is changed to 1-84. Eighty holes of 700 µm in diameter are used for the next experiment. Cellulose dope is poured in the center of a spinning rotor at 120 degreeC. The released thin dope strands fall by gravity into the room temperature water in the basin around the rotor. Here they are reproduced. Although several fibers are bonded to each other, most of the fibers are kept individually and are several centimeters in length.

In addition to the preceding process, very similar microdenier fibers are successfully produced from bleached and non-bleached kraft pulp, sulfurous acid pulp, microcrystalline cellulose, and blends of up to 30% corn starch or polyacrylic acid and cellulose.

The diameter (denier) of the fiber can be easily adjusted by various means. If the dope viscosity is large, the fiber is thick. The dope viscosity can be controlled by the cellulose solids content or the degree of cellulose polymerization. If the spin hole size is small or the drum rotation is small, the fiber diameter is small. 5-20 μm (0.2-3.1 denier) fibers and 20-50 μm (3.1-19.5 denier) fibers can be easily formed. Fiber lengths vary depending on the process parameters and geometry of the system.

Example 3 Fabrication by Melt Blowing

The dope of Example 1 is maintained at 120 ° C. and fed to an apparatus developed for forming a meltblowing synthetic polymer. The total pore length is 50 mm and has a diameter of 635 μm tapered to 400 μm at the discharge end. After a distance of air movement of about 20 cm in the disturbed air blast, the fibers are dropped into the water tank for regeneration. The regenerated fiber length is variable. Some short fibers are formed but usually have a length of several tens of centimeters. Changes in the extrusion parameters allow continuous fibers to form. Surprisingly, the cross section of the fiber is not uniform along the fiber length. This fiber is very similar to natural fiber in its overall shape, so this feature is advantageous when spinning the yarn using the microdenier material of the present invention.

The fibers impinge on the moving stainless steel mesh belt before they are introduced directly into the regeneration tank. A well bonded nonwoven mat is formed.

The lyocell nonwoven does not need to be self bonding. They may be partially bonded or not self bonded at all. In this case they may be bonded by hydroentangling with adhesive binders such as starch or various polymer emulsions.

The process of Example 1 is repeated using microcrystalline cellulose furnish over wood pulp to increase the solids content of the dope. The product used is Avicel Type pH-101 microcrystalline cellulose from FMC Corp. (Newwark. Delaware). Dopes are prepared using 15 g and 28.5 g (dry weight) of microcrystalline cellulose with 66.2 g of 97% NMMO, 24.5 g of 50% NMMO and 0.05 g of propyl gallate. The procedure is described in Example 1. The resulting dope contains 14% and 24% cellulose, respectively. These are melt blown as in Example 3. The resulting fiber has the same shape as Examples 2 and 3.

Fiber denier depends on adjustable factors. Among these are the solution solids content, solution pressure and temperature in the compressor head, pore diameter, air pressure, and other variables known in the meltblowing and centrifugal spinning techniques. Lyocell fibers of an average of 0.5 denier or less can be produced consistently by meltblowing or centrifugal spinning techniques. The 0.5 denier fiber corresponds to an average diameter of about 7-8 μm (estimated based on the equivalent circular cross-sectional area).

The fibers of the present invention are studied by X-ray analysis for crystallinity and microcrystalline morphology. Comparisons with other cellulose fibers shown in the following table are also made. Data for micro denier fibers is taken from the centrifugal fibers of Example 2.

Table 1

Crystalline Properties of Various Cellulose Fibers

Fiber Pattern Micro Denier Fiber Common Lyocell Tencel Cotton

Crystallinity Index 67% 65% 70% 85%

Small Crystalline Cellulose II Cellulose II Cellulose II Cellulose I

The following strength is estimated as it is difficult to measure the tensile strength of individual fibers. The micro denier fibers of the present invention are compared with other fibers.

Centrifugal spinning lyocells with an average diameter of 5 μm correspond to 0.25 denier fibers.

The rough surface of the fibers of the present invention results in low gloss without internal degloss. Since gloss is a difficult property to measure, the following test shows the difference between the fiber produced by the method of Example 2 and a commercial lyocell fiber. A small wet sheet is made of each fiber and the reflectance is measured. The reflectance of Example 2 is 5.4% and the commercial fiber is 16.9%.

The dope is prepared in the following manner. 2300 g dry NB416 kraft pulp is mixed with 14 kg of 5.0% sulfuric acid solution in a plastic container. The average D.P. of NB416 not dried before acid treatment is 1400, hemicellulose content is 13.6% and copper value is 0.5. The pulp and acid mixture is maintained at 97 ° C. for 1.5 hours, cooled at room temperature for 2 hours and washed with water until the pH is 5.0-7.0. The average D.P. of acid treated pulp is 600 as determined by ASTM D1795-62 and the hemicellulose content is 13.8% (the difference between D.P. of acid treated and untreated pulp is not statistically significant). The copper value of the acid treated pulp is 2.5.

Acid treated pulp is dried and some is dissolved in NMMO. 9 g of dried, acid treated pulp is dissolved in 61.7 g of 97% NMMO, 21.3 g of 50% NMMO and 0.025 g of propyl gallate mixture. The flask containing the mixture is placed in an oil bath at 120 ° C. and stirring for 0.5 hours is continued.

The resulting dope is maintained at 120 ° C. and fed to a single hole laboratory meltblowing head. In the nozzle hole, the diameter is 483 μm, the length is 2.4 mm, and the L / D is 5. The removable coaxial capillary, located just above the hole, is 685 μm long and 80 mm long and L / D 116. The transition zone angle between the hole and the capillary is 118 °. The air delivery ports are parallel slots with holes located equidistantly between them. The air gap is 250 μm wide and the nose area is 1.78 mm wide. The angle between the air slot and the centerline of the capillary and nozzle is 30 °. The dope is supplied to the extrusion head by a positive displacement piston pump activated by a screw. The air velocity measured with the hot wire instrument is 3660 m / min. The air is warmed to 60-70 ° C. at the discharge point in the electrically heated extrusion head. The temperature in the capillary without dope is 80 ° C. at the inlet end and 140 ° C. just before the nozzle outlet. Doping temperature measurements in nozzles and capillaries under process conditions are not possible. In equilibrium conditions continuous fibers are formed with dope. The yield is somewhat variable to achieve a similar fiber diameter with each dope, but is more than 1 g of dope per minute. In optimal running conditions the fiber diameter is 9-14 μm.

Fine water spray is directed at the descending fiber at a point below 200 mm of the extrusion head and the fiber is trapped on a roll operating at a surface speed of 1/4 of the descending fiber linear velocity.

If the capillary zone of the head is removed, continuous fibers in the cotton denier range cannot be formed. Capillaries are important for continuous fiber formation and reduced die swelling.

Fiber denier depends on adjustable factors. Among these are the solution solids content, solution pressure and temperature in the compressor head, pore diameter, air pressure, and other variables known in the meltblowing and centrifugal spinning techniques. Lyocell fibers in the cotton fiber range (average diameter of 10-20 μm) can be consistently produced by meltblowing techniques with a dope yield of at least 1 g / min per hole.

The dope is prepared in the following manner. 2300 g dry NB416 kraft pulp is mixed with 14 kg of 5.0% sulfuric acid solution in a plastic container. The average D.P. of NB416 not dried before acid treatment is 1400, hemicellulose content is 13.6% and copper value is 0.5. The pulp and acid mixture is maintained at 97 ° C. for 1.5 hours, cooled at room temperature for 2 hours and washed with water until the pH is 5.0-7.0. The average D.P. of acid treated pulp is 600 as measured by ASTM D1795-62 and the hemicellulose content is 13.8% (difference between D.P. of acid treated and untreated pulp is not statistically significant). The copper value of the acid treated pulp is 2.5.

The acid treated pulp is reduced to a copper value of 0.6 with NaBH 4 , washed to pH 6-7, dried and some dissolved in NMMO. 9 g of dried, acid treated pulp is dissolved in 1100 g of NMMO and 0.25 g of propyl gallate mixture. The stainless steel beaker containing the mixture was placed in an oil bath at 120 ° C. and stirring continued for 1 hour.

The resulting dope is maintained at 120 ° C. and fed to a 20 hole laboratory meltblowing head. In the nozzle hole, the diameter is 400 μm, the length is 2.0 mm and the L / D is 5. The removable coaxial capillary, located just above the hole, is 626 μm in diameter 20 mm long and 32 L / D. The transition zone angle between the hole and the capillary is 118 °. The air delivery ports are parallel slots with holes located equidistantly between them. The air gap is 250 μm wide and the nose area is 1.0 mm wide. The angle between the air slot and the centerline of the capillary and nozzle is 30 °. The dope is supplied to the extrusion head by a positive displacement piston pump activated by a screw. The air velocity measured with the hot wire instrument is 3660 m / min. The air is warmed to 60-70 ° C. at the discharge point in the electrically heated extrusion head. The temperature in the capillary without dope is 80 ° C. at the inlet end and 130 ° C. just before the nozzle outlet. Doping temperature measurements in nozzles and capillaries under process conditions are not possible. In equilibrium conditions continuous fibers are formed with dope. The yield is somewhat variable to achieve a similar fiber diameter with each dope, but more than 0.6 g of dope per minute per hole. In optimal running conditions the fiber diameter is 9-14 μm.

Fine water spray is directed at the descending fiber at a point below 200 mm of the extrusion head and the fiber is trapped on a roll operating at a surface speed of 1/4 of the descending fiber linear velocity.

If the capillary zone of the head is removed, continuous fibers in the cotton denier range cannot be formed. Capillaries are important for continuous fiber formation and reduced die swelling.

Fiber denier depends on adjustable factors. Among these are the solution solids content, solution pressure and temperature in the compressor head, pore diameter, air pressure, and other variables known in the meltblowing and centrifugal spinning techniques. Lyocell fibers in the cotton fiber range (average diameter of 10-20 μm) can be consistently produced by meltblowing techniques with a dope yield of at least 0.6 g / min per hole.

Comparative Example 1: Preparation of TITK lyocell fibers used for calculating the coefficient of variability along the fiber length

Tencel fiber is commercially available. Samples used are obtained from the International Textile Center (ITC) of Acoridis and Texas Tech University. Tencel A-100 is obtained from Acoridis (UK).

Example 8 Calculation of Variable Coefficients Along Fiber Length

Sample fibers are randomly selected from the fibers obtained by the methods of Example 5-7 and Comparative Example 1-2. Cut the fibers to 2 inches or less. Less than 200 are taken from the cut fiber samples. An optical microscope is used for the diameter measurement. An alternative lens is mounted on the microscope for fiber diameter reading. A magnification of 1060 is used to accurately measure the diameter. The diameter is read every hundredths of an inch along the fiber length. The diameter is from one side of the fiber to the opposite side. The average diameter is calculated by dividing the sum of all diameters by the number of readings. The standard deviation is calculated for each reading. The coefficient of variability (CV) is the sum of the standard deviations divided by the mean diameters. The percentage is obtained by multiplying this number by 100.

CV results are presented in Table 3. The highest CV at 25.4% from the data in Table 3 is the centrifugal fiber and has an average diameter of 11.5 microns. For meltblowing fibers, the best CV is 14.8% and the diameter is 24.5 microns. Meltblowing fibers with an average diameter of 13-14 microns provide a CV of 13.6-13.7%. Large and small meltblowing fibers provide a relatively small CV. Continuously drawn TITK fibers have a CV of 5.4-6.1%. Continuously drawn Tencel and Tencel A-100 fibers showed CVs of 5.2 and 5.9%. Meltblowing fibers and centrifugal fibers have a higher CV than continuous drawn lyocell fibers.

TABLE 3

Diameter variability along fiber length

Fiber Diameter (microns) CV (%)

Melt Blowing (1 hole) 13.7 13.6

Melt Blowing (1 hole) 24.9 14.8

Melt Blowing (20 holes) 13.1 13.7

Melt Blowing (20 holes) 30.7 12.6

Melt Blowing (20 holes) 5.5 7.6

Centrifugal spinning 34.2 10.9

Centrifugal radiation 17.5 14.3

Centrifugal spinning 11.5 24.4

TITK LIOcell 13.0 6.1

TITK LIOcell 13.5 5.4

Tencel 13.5 5.2

Tencel A-100 10.8 5.9

Claims (14)

Lyocell fibers characterized by having a variability coefficient of 6.5-25.4%

The cross-sectional configuration variability and cross-sectional diameter variability according to the length of the lyocell fibers of claim 1 is greater than the cross-sectional configuration variability and cross-sectional diameter variability according to the length of the lyocell fibers produced by the continuous drawing process. Featured lyocell fiber

The lyocell fiber of claim 1 wherein the lyocell fiber comprises a fiber mixture greater than 0 and less than 1 denier in diameter.

Spun yarn comprising lyocell fibers of claim 1

The lyocell fiber of claim 1 wherein the fibrillation tendency under wet wear conditions is high and the dye solubility is high.

2. The lyocell fiber of claim 1 wherein the individualized and continuous

The lyocell fiber of claim 1, wherein the lyocell fiber has an average diameter of 5.5 microns.

The lyocell fiber of claim 1, wherein the lyocell fiber has a modulus of variability of 6.5%.

The lyocell fiber of claim 1, wherein the lyocell fiber has a modulus of variability of 7.0%.

The lyocell fiber of claim 1, wherein the lyocell fiber has a modulus of variability of 10%.

The lyocell fiber of claim 1 wherein the fiber is melt blown.

12. The lyocell fiber of claim 11 wherein said lyocell fiber has a variability coefficient of 12.6%.

The lyocell fiber of claim 1 wherein the fiber is centrifuged.

14. The lyocell fiber of claim 13 wherein said lyocell fiber has a coefficient of variability of 10.9%.